This invention relates to an electrochemical system, e.g. a fuel cell system, an electrochemical compressor or an electrolyzer, with an end plate and a stack cover plate as described in the introductory portions of the independent claims.
Electrochemical systems of the prior art conventionally have two end plates, between which a plurality of metal separator plates or bipolar plates are located in a stack. Neighboring separator plates thereby normally enclose electrochemical cells in which chemical energy is converted into electrical energy or vice-versa. Likewise, the electrochemical cells can be used to electrochemically increase the pressure in a hydrogen system. For this purpose it is necessary for the system to have electrical conductors that connect to the electrodes of the electrochemical cells with an outside of the system, and by means of which an electrical voltage can be applied to the electrodes or can be picked up. These conductors are then typically connected or can be connected with an electrical consumer or with an electrical voltage source.
Conventionally the supply or discharge of electrical energy or the application or pickup of the electrical voltage to or from the electrochemical system takes place via at least one of the end plates and via the separator plate adjacent to this end plate. The latter is also called the cover plate, cover separator plate or optionally the cover bipolar plate because it covers the plate stack toward the respective end plate. The electrical connection between the cover plate and the outside of the electrochemical system is conventionally established by means of a metallic current lead on a side of the end plate facing the cover plate and via an electrically conductive gas diffusion layer or GDL that is located between the current lead and the cover plate and is in electrical contact with the latter. The current lead is connected with the outside of the system, e.g. by means of an electrical cable. The gas diffusion layer is conventionally in the form of a fabric or similar structure containing graphite.
However, it has been repeatedly shown that high ohmic losses occur with this type of electrical contact with electrodes of the electrochemical cells of the plate stack.
Conventionally, both the end plate as well as the cover plate have openings for reaction media and coolant, each of which openings is sealed. If, as is conventional, the end plate is manufactured from a polymer material and the cover plate is metal, significantly different expansions and contractions occur during the heating and cooling of the electrochemical system which destroy the sealing devices of the prior art, so that the seal of the electrochemical system is not guaranteed in the long term.